AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Distinct Seasonal Differences in Secondary Organic Aerosol Formation from In-situ Oxidation of Near-highway Air
PROVAT SAHA, Stephen Reece, Andrew Grieshop, North Carolina State University
Abstract Number: 475 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Motor vehicles are a major source of primary aerosols and secondary aerosol precursors. However, the extent to which motor vehicles contribute to ambient SOA production remains highly uncertain. Here, we present in-situ measurements of secondary organic aerosol (SOA) formation using an Oxidation Flow Reactor (OFR) from summer and winter field campaigns at a site 10 m from Interstate 40, outside Durham, North Carolina. In July-2015 (summer) and February-2016 (winter), ambient air at this near-highway site was exposed to high oxidant (O3 and OH; hydroxyl radical) concentrations in an OFR. Submicron aerosol chemical composition, size distributions, and volatility using a thermodenuder were measured alternatively between the OFR-processed and ambient air (bypass). Results from this study show substantial seasonal differences in SOA formation upon OFR-oxidation. While a peak enhancement of OA mass concentration of ~ 3-10 μg m-3 was observed during summer campaign with 2-5 days of equivalent atmospheric aging, very low enhancement (~0.5 μg m-3) was observed during winter. In contrast, measurement at both seasons show nearly consistent changes of O:C and H:C in bulk OA with OH exposures in OFR. Substantial SOA formation during summer-time and very low at winter-time suggest that biogenic emissions, which have a very strong dependence on temperature, make the dominant contribution to observed OFR-SOA production in this near-road site. These results highlight the utility of the OFR for studying the prevalence of SOA precursors in complex real-world settings.